Fuel injection system for two cycle engine

ABSTRACT

A low pressure fuel injection system for a two cycle internal combustion engine. Fuel is introduced into the combustion chamber during the intake cycle from a cavity in the wall of the combustion chamber supplied with fuel by metering apparatus that controls the flow of fuel in accordance with engine demand. The fuel is compressibly accumulated when the cavity is covered by the piston during the compression and combustion cycles. As the piston moves into the fuel intake cycle, the cavity is opened and the fuel charge is discharged therefrom and swept out by the flow of intake air for subsequent vaporization and combustion.

United States Patent [1 1 Reese et al.

1 FUEL INJECTION SYSTEM FOR TWO CYCLE ENGINE [75] Inventors: Gerald D. Reese; Gerald G. Shank, both of Roseau; Lowell D. Carlson, Pencer, all of Minn.

173] Assignee: Textron Inc., Providence. R1.

[22] Filed: June 1, 1972 [21] Appl. No.: 258,805

Related U.S. Application Data [621 Division of Ser. No, 58,431, July 27, 1970, Pat. No,

[52] U.S. CL... 123/32 A; 123/73 CA; 123/139 AJ [51] Int. Cl. F02b l5/00; FOZrn 69/10 [581 Field of Search 173/73 C, 73 CA, 73 CB, 173/73 CC, DIG. 5, 139 A], 32 A [56] References Cited UNITED STATES PATENTS 661,599 11/1900 Day 123/73 C 840,178 H1907 Tuttle r 123/73 CB X 977,847 12/1910 Wright t r 123/73 CA X 1,143,258 6/1915 Dunham 123/73 C X 3,190,271 6/1965 Gudmundsen 123/73 C X 1 June 10, 1975 3.l98,l80 8/1965 Pose 123/69 R X FORElGN PATENTS OR APPLICATIONS 13,211 8/1904 Norway 123/73 C Primary Examiner-Charles .l. Myhre Assistant Examiner-W. Rutledge, Jr.

Attorney, Agent, or Firm-Merchant, Gould, Smith & Edell [57] ABSTRACT A low pressure fuel injection system for a two cycle internal combustion engine. Fuel is introduced into the combustion chamber during the intake cycle from a cavity in the wall of the combustion chamber supplied with fuel by metering apparatus that controls the flow of fuel in accordance with engine demand. The fuel is compressibly accumulated when the cavity is covered by the piston during the compression and combustion cycles. As the piston moves into the fuel intake cycle, the cavity is opened and the fuel charge is discharged therefrom and swept out by the flow of intake air for subsequent vaporization and combustion.

10 Claims, 7 Drawing Figures I FUEL INJECTION SYSTEM FOR TWO CYCLE ENGINE This application is a division of our copending application Ser. No. 58,431, which was filed on July 27, 1970 and issued on Dec. 26, 1972 as U.S. Pat. No. 3,707,l43.

The invention is directed to a low pressure fuel injection system for an internal combustion engine which is particularly useful in a two cycle internal combustion engine.

The advantages of direct cylinder fuel injection have long been known, particularly with regard to crankcase scavenged two cycle internal combustion engines. For instance, because the reciprocating piston in a two cycle engine performs the function of closing and opening the several valve ports, the order of control is reversed as the piston changes directions. At one point during the fuel and air intake cycle of a conventionally fueled two cycle engine, the transfer and exhaust ports are opened simultaneously and a portion of the combined fuel-air charge entering through the transfer port is lost to atmosphere before the exhaust port closes. This fuel loss occurs even at the engine design speed, which normally occupies a range of [,000 to 1,500 rpm s; but the problem worsens considerably at speeds outside this optimum operating range. The result is a significant decrease in both engine efficiency and economy of operation. Also of considerable significance is the hydrocarbon emission which results from the exhaust of unburned fuel to the atmosphere. Although these problems are significant only at speeds outside the design speed range, few engines operate in that range the majority of the time. Fuel injection alleviates these problems because it permits the fuel to be admitted to the chamber at a time or location such that it is impossible for fuel to be lost through the exhaust port.

Another advantage of fuel injection arises from the fact that in conventional two cycle operation the fuelair charge is drawn through the crankcase. Even with direct oil injection to the main bearings of the engine, the oil is immediately diluted by the fuel. Consequently, a lubricant having a relatively high viscosity rating is required under these conditions. Fuel injection eliminates the fuel from the crankcase area and permits usage of a lubricant having a lower viscosity, which enhances cold weather operation of the engine and oil injection system. Further, the elimination of lubricant dilution allows a reduction in the volume of lubricant necessary to satisfactorily lubricate the engine components.

Another advantage realized by direct cylinder fuel injection results from the location at which fuel vaporization takes place. The vaporization of fuel into a gaseous state requires absorption of a considerable amount of heat. Under conventional two cycle operation, the vaporizing fuel absorbs heat from the crankcase, where heat problems ordinarily do not exist. With direct cylinder fuel injection, the fuel is vaporized in the combustion chamber where it absorbs heat from the piston, cylinder walls and cylinder head, all of which operate at extremely high temperatures. Fuel injection thus enables operation at higher combustion temperatures and lower component temperatures and results in increased efficiency.

Further, due to the erratic flow of fresh fuel-air charge through the transfer ports into the combustion chamber, conventional two cycle engines that are designed for high specific power output tend to have poor low speed and idle characteristics. Properly timed injection of fuel into the cylinder in precisely metered amounts improves these low speed characteristics.

Lastly, since no fuel is admitted through the air inlet in fuel injected systems there is no back flow of vaporized fuel through the air inlet port. This greatly simplifies the design of air cleaners and sound attenuators.

Notwithstanding these considerable advantages, fuel injection is rarely used on two cycle engines. The major problem that has precluded its application has been the extremely short cycle time involved and the resultant short period of time in which the fuel can be injected. For example, in a two cycle 8000 rpm engine the time alloted for the injection cycle cannot exceed approximately 1 10 of crankshaft rotation, and injection must take place 8000 times per minute.

To the best of our knowledge, there is no simple, low pressure fuel injection system available for a two cycle engine. In order to impart to a predetermined quantity of fuel the momentum necessary to overcome its inertia and effect its injection into the combustion chamber during sucha short period of time (which is on the order of a few milliseconds), it is necessary to use extremely high pressure equipment which is both complex and costly. Although satisfactory operation is possible with such high pressure systems, their cost often approaches or exceeds the manufacturing cost of the engine itself. An example of such a complex system is shown in U.S. Pat. NO. 3,198,180, issued Aug. 3, 1965.

We have found that by deviating from the usual procedure of forcibly injecting a quantity of fuel into the cylinder during the normal injection cycle, we can achieve the intended results with a minimum of components that are economical and simple to produce and operate. Rather than injecting fuel into the cylinder only during the short degree of crankshaft rotation previously assumed to be mandatory, our procedure is to begin injecting fuel into a small pocket or cavity in the cylinder wall during the time the cavity is covered by the piston; viz., during the compression and combustion cycles. Since a small volume of air is trapped in the cavity when it is covered by the piston, the fuel is compressed as it enters. During the air transfer period, the piston uncovers the cavity and the fuel is carried out for vaporization and combustion. Our testing makes it appear that the fuel is carried from the cavity immediately by the combined effects of pressure build-up in the cavity and air flow in the chamber from the transfer port. Part of the pressure in the cavity may be caused by vaporization of a portion of the fuel in the cavity by the hot cylinder wall.

Because fuel accumulates in the cavity during the longer off-injection cycle, there is no need for expensive, high pressure pumps to force fuel into the cavity. Instead, in the preferred embodiment, we employ an inexpensive impulse pump which is operated by crankcase pressure. Although the impulse pump is preferred, it is also possible to use a gravity feed to the cavity if a sufficient pressure head exists between the fuel level and engine.

Coupled with appropriate fuel metering apparatus, the inventive low pressure fuel injection system provides a simple, economical and sound method of injecting fuel into the cylinder at the proper time and at the proper volume for an extreme range of operating conditions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a two cycle engine and fuel injection system embodying the inventive principle, part thereof being broken away, said engine operating in its combustion cycle.

FIG. 2 is a view similar to FIG. 1 but showing only a portion thereof, the engine entering its exhaust cycle.

FIG. 3 is similar to FIG. 2, but with the engine enter ing its air intake cycle;

FIG. 4 is a view similar to FIG. 2, but with the engine entering its fuel intake cycle;

FIG. 5 is a view similar to FIG. 2, but with the engine entering its compression cycle;

FIG. 6 is an enlarged fragmentary view of the engine cylinder wall, showing with particularity a fuel injection cavity or recess; and

FIG. 7 is a further enlarged sectional view of the fuel injection cavity taken generally along the line 7-7 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, an engine represented generally by the numeral II is shown to comprise an engine block 12 having a crankcase chamber (not shown), and a housing or cylinder head 13 which defines a cylindrical combustion chamber 14. A piston 15 is arranged to reciprocate in combustion chamber 14 by virtue of its pivotal connection to a crankshaft 16 through a connecting rod 17. A conventional fly wheel 18 is rotatably mounted on crankshaft l6 and carries a pulley 19 which drives an oil injecting pump 21 by a belt 22. Oil pump 21 receives a supply of oil from the engine crankcase, and pumps it through an oil line 23 to the main bearings (not shown) of crankshaft 16 for purposes of lubrication.

Opening on the inner cylindrical face of combustion chamber 14 is an air inlet port 24 which communicates with atmosphere through an air horn 25. A butterfly valve 26 is rotatably disposed in air horn 25 and serves to vary the volume of air entering air horn 25 in the usual throttling fashion. Valve 26 is rotatable by a manual control (not shown) to vary the speed of engine 11, as described below.

Also opening on the inner cylindrical face of combustion chamber 14 are an air transfer port 27 and an exhaust port 28, the former of which communicates with the engine crankcase by a passage (not shown) formed in the engine block 12. As FIG. 1 indicates, the top of transfer port 27 is disposed slightly below the top of exhaust port 28 with respect to the cylinder axis, and air inlet port 24 is located a distance below transfer port 27.

A threaded opening 29 is formed in the top of cylinder head 13 to receive a spark plug 31.

Fuel is admitted to combustion chamber 14 from a cavity 32 which is formed in the inner cylindrical face of combustion chamber 14. In FIGS. 1-5, the size of cavity 32 is exaggerated for purposes of clarity. In FIGS. 6 and 7 cavity 32 is shown in its preferred form, being generally concave in shape and having a relatively large cross sectional area as compared to its shallow depth. This configuration permits fuel accumulated in cavity 32 to be quickly discharged into combustion chamber 14 when uncovered by piston 15.

With respect to the cylindrical axis, cavity 32 is disposed between air inlet port 24 and the top of transfer port 27 and is of sufficient size to hold a fresh charge of fuel for subsequent vaporization and combustion in combustion chamber 14. Cavity 32 is connected to a fuel metering apparatus, represented generally by the numeral 33, by a passage 30 in cylinder head I3, to which is connected a conduit 34 which includes a ball type check valve 35.

Metering apparatus 33 consists of an adjustable main flow valve 36 and an adjustable idle flow valve 37 connected in parallel therewith. Main flow valve 36 is controlled through a linkage 38 by a conventional diaphragm actuator 39 which senses crankcase pressure through a conduit 41. Idle flow valve 37 is opened approximately one quarter of a turn with movement of butterfly valve 26 by the manual throttle control through a linkage 42.

Metering apparatus 33 receives a supply of fuel from a conventional impulse pump 43, which is also actuated by crankcase pressure through a conduit 44. Pump 43 is adapted for connection to a source of fuel through a fuel line 45.

In operation, it is initially assumed that a fresh charge of fuel and air has already been admitted to combustion chamber, and engine 11 has compressed the charge and is entering the combustion cycle as shown in FIG. 1. At this point, piston 15 is blocking transfer port 27, exhaust port 28 and cavity 32, and the engine ignition system causes spark plug 31 to ignite the mixture. The resulting combustion begins to drive piston 15 downward through its power stroke.

As shown in FIG. 1, when piston 15 is in its upper position, air can be drawn in through air horn 25, butterfly valve 26 and air inlet port 24 to the crankcase. As piston 15 moves downward, air inlet 24 is sealed and pressure within the crankcase begins to increase. This increasing pressure is sensed by impulse pump 43 which pumps a discrete quantity of fluid through metering apparatus 33. The increasing crankcase pressure is also sensed by diaphragm actuator 39, which causes linkage 38 to open main flow valve 36 and pass the discrete quantity of fuel through conduit 34 to cavity 32. Preferably, conduit 41 includes a check valve (not shown), or the like, which rectifies the positive and negative pulsing pressure transmitted therethrough, resulting in application of a steady pressure to diaphragm actuator 39 which varies as a function of engine speed. A bleed port (not shown) continuously bleeds pressure in conduit 41 and diaphragm actuator 39 to atmosphere, thereby permitting a controlled pressure buildup as engine speed and crankcase pressure increase. Pump 43 is capable of providing a pulsating flow of fuel greater than the amount required by the engine, but its output is restricted by the position of main flow valve 36. Hence, in response to a given piston stroke, piston 43 provides a discrete quantity of fuel which passes through main flow valve 36 and is accumulated in cavity 32.

Because residual air has been caught in cavity 32 and held thereby the face of the piston 15, the discrete quantity of fuel is lightly compressed therein. Check valve 35 prevents fuel from backing up in conduit 34 once it has been pumped into cavity 32.

As piston continues to move downward, exhaust port 28 is the first port to be uncovered (FIG. 2), and exhaust of the combusted gas mixture begins. This movement of exhaust gases is assisted with the opening of transfer port 27, as shown in H6. 3, by the entrance of fresh air from the crankcase into compression chamber 14. Transfer port 27 is designed to direct the fresh air charge through a loop scavenged path, whereby the air passes up the cylinder wall opposite exhaust port 28, across the cylinder head and down the opposite cylinder wall to exhaust port 28. This movement of fresh air assists in driving the combusted fuel mixture out exhaust port 28.

As shown in FIG. 4 piston 15 continues its downward movement to bring the pressure in the engine crankcase to a maximum, and, through impulse pump 43 and metering apparatus 33 thereby accumulate a quantity of fuel under pressure in cavity 32. Piston 15 then uncovers cavity 32, discharging the fuel therein and permitting it to mix with the fresh air charge entering compression chamber 14 through transfer port 27. Cavity 32 is positioned on the cylinder wall of compression chamber 14 so that the leading side of the air transfer pattern, which may escape through exhaust portion 28 before it is closed, carries no fuel vapor. Consequently, none of the fuelair mixture reaches the open exhaust port before the compression cycle begins. This enhances fuel economy and diminishes the problem of hydrocarbon emission into the atmosphere.

FIG. 5 shows piston 15 after it has moved through the cycle of air and fuel intake, and as it begins the compression cycle with the closing of cavity 32, air transfer port 27 and exhaust port 28. Further upward movement of piston 15 carries it to the position shown in FIG. 1, and the two cycle process continues.

From the operational description of engine 11, it may be observed that the intake cycle includes separate intakes of fuel and air and begins as piston 15 moves downward to uncover transfer port 27. The intake cycle continues as cavity 32 is uncovered and terminates as piston 15 reverses direction, covering cavity 52 and, finally, transfer port 27.

The compression cycle begins as piston 15 continues upward and completely covers exhaust port 28, and

ends as piston 15 reaches its upper most position in chamber 14.

The combustion cycle begins with ignition of the fuel charge by spark plug 31, which is at or near the end of the compression cycle. The combustion cycle continues with downward movement of piston 15 and ends as exhaust port 28 is opened, at which time the exhaust cycle begins. The exhaust cycle completely encompasses the intake cycle in regard to time, extending through the opening and closing of both transfer port 28 and cavity 32 and terminating as piston 15 moves upward to close exhaust port 28.

At idling speed, idle flow valve 37 is adjusted to provide sufficient fuel along with the volume of air entering through butterfly valve 26. Main flow valve 36 is adjusted so that the crankcase pressure operating on diaphragm actuator 39 through linkage 38 is insufficient to open it. During the initial stage of acceleration, the linkage 42 between butterfly valve 26 and idle flow valve 37, opens valve 37 approximately one quarter of a turn until the engine demand, as reflected by crankcase pressure, builds up sufficiently to drive actuator 39. The aforementioned bleed port in diaphragm actuator 39 reduces the control pressure therein as engine speed and crankcase pressure decrease, thus enabling main flow valve 36 to move toward a closed position and thereby diminish the output of pump 43.

lt will be appreciated that the inventive principle of providing a fuel accumulating cavity proximate the combustion chamber, and accumulating fuel therein at a time other than during the intake cycle for subsequent free and instantaneous discharge during the intake cycle, is applicable to engines other than two cycle engines; and such other engines can benefit equally through the elimination of costly high pressure pumping equipment and simpler fuel control.

It is evident that the particular type of metering apparatus used is unimportant so long as it provides the function of metering fuel for accumulation in cavity 32 during the compression and combustion cycles. Of primary importance is the provision of structure, such as a cavity proximate the combustion chamber, for the accumulation of fuel during the compression and combustion cycles, which accumulation is disposed sufficiently close to compression chamber 14 to allow the accumulated fuel to be freely and instantaneously discharged into the compression chamber 14 without having to impart great inertial energy to the fuel charge.

What is claimed is:

1. A method of low pressure injection of ignitable fuel under the combustion chamber of an internal combustion engine operable through cycles of intake, compression, combustion and exhaust and which includes piston means sealably movable to vary the volume of the combustion chamber, means for supplying air to the combustion chamber during the intake cycle and means for exhausting combustion gases from the combustion chamber during the exhaust cycle, comprising:

a. supplying to and accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is sufficiently close to the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being supplied and accumulated at a time other than during the intake cycle;

b. blocking fluid communication between the combustion chamber and the storage cavity for a time other than during the intake cycle;

c. establishing fluid communication between the combustion chamber and the storage cavity during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit free and instantaneous discharge into the combustion chamber;

d. and supplying air to the combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being subsequently mixed in the combustion chamber for ignition and combustion therein.

2. The method defined by claim 1, in which the internal combustion engine operates through combined cycles of intake, compression, combustion and exhaust, and fluid communication between the combustion chamber and the storage cavity is blocked during the compression and combustion cycles, the quantity of fuel being accumulated during at least a portion of the time such fluid communication is blocked.

3. The method defined by claim 1, wherein fuel is supplied to the storage cavity as a function of engine demand.

4. The method defined by claim 1, in which the internal combustion engine operates through combined cycles of intake, compression, combustion and exhaust and the piston means is sealably movable to vary the volume of the combustion chamber and a crankcase, and further comprising the step of metering the flow of fuel to the storage cavity as a function of pressure in the engine crankcase.

5. The method defined by claim 4, and further comprising the step of pumping fuel to the storage cavity as a function of pressure in the engine crankcase.

6. The method defined by claim 1, wherein the entire quantity of fuel is accumulated in a storage cavity the entirety of which is on the face of the combustion chamber wall.

7. A method of low pressure injection of ignitable fuel into the combustion chamber of an internal combustion engine operable through cycles of intake, compression, combustion and exhaust, comprising:

a. accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is sufficiently close to the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being accumulated at a time other than during the intake cycle;

b. establishing communication between the storage cavity and the combustion chamber during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit its free and instantaneous discharge into the combustion chamber;

0. and supplying air to the engine combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being subsequently mixed in the combustion chamber for ignition and combustion therein.

8. The method defined by claim 7, wherein the entire quantity of fuel is accumulated in a storage cavity the entirety of which is on the face of the combustion chamber wall.

9. A method of low pressure injection of ignitable fuel into the combustion chamber of a two cycle internal combustion engine operable through combined cycles of intake, compression, combustion and exhaust and which includes a reciprocating piston sealably movable between a cylindrical combustion chamber and a crankcase chamber to vary the volume thereof, an air inlet port opening on the cylindrical wall of the combustion chamber which communicates with the crankcase chamber through an air transfer passage and an exhaust port opening on the cylindrical wall of the combustion chamber which communicates with atmosphere, comprising:

a. accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is disposed on the face of the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being metered through the storage cavity as a function of pressure in the crankcase chamber and accumulated in the storage cavity at a time other than during the intake cycle;

b. blocking fluid communication between the combustion chamber and the storage cavity for a time other than during the intake cycle;

c. establishing fluid communication between the combustion chamber and the storage cavity during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit its free and instantaneous discharge into the combustion chamber;

d. and supplying air to the combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being substantially mixed in the combustion chamber for ignition and combustion therein.

10. The method defined by claim 9, wherein the quantity of fuel is accumulated in the storage cavity relative to the piston so that the piston blocks and establishes communication between the combustion chamber and the entire quantity of fuel. 

1. A method of low pressure injection of ignitable fuel under the combustion chamber of an internal combustion engine operable through cycles of intake, compression, combustion and exhaust and which includes piston means sealably movable to vary the volume of the combustion chamber, means for supplying air to the combustion chamber during the intake cycle and means for exhausting combustion gases from the combustion chamber duRing the exhaust cycle, comprising: a. supplying to and accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is sufficiently close to the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being supplied and accumulated at a time other than during the intake cycle; b. blocking fluid communication between the combustion chamber and the storage cavity for a time other than during the intake cycle; c. establishing fluid communication between the combustion chamber and the storage cavity during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit free and instantaneous discharge into the combustion chamber; d. and supplying air to the combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being subsequently mixed in the combustion chamber for ignition and combustion therein.
 2. The method defined by claim 1, in which the internal combustion engine operates through combined cycles of intake, compression, combustion and exhaust, and fluid communication between the combustion chamber and the storage cavity is blocked during the compression and combustion cycles, the quantity of fuel being accumulated during at least a portion of the time such fluid communication is blocked.
 3. The method defined by claim 1, wherein fuel is supplied to the storage cavity as a function of engine demand.
 4. The method defined by claim 1, in which the internal combustion engine operates through combined cycles of intake, compression, combustion and exhaust and the piston means is sealably movable to vary the volume of the combustion chamber and a crankcase, and further comprising the step of metering the flow of fuel to the storage cavity as a function of pressure in the engine crankcase.
 5. The method defined by claim 4, and further comprising the step of pumping fuel to the storage cavity as a function of pressure in the engine crankcase.
 6. The method defined by claim 1, wherein the entire quantity of fuel is accumulated in a storage cavity the entirety of which is on the face of the combustion chamber wall.
 7. A method of low pressure injection of ignitable fuel into the combustion chamber of an internal combustion engine operable through cycles of intake, compression, combustion and exhaust, comprising: a. accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is sufficiently close to the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being accumulated at a time other than during the intake cycle; b. establishing communication between the storage cavity and the combustion chamber during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit its free and instantaneous discharge into the combustion chamber; c. and supplying air to the engine combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being subsequently mixed in the combustion chamber for ignition and combustion therein.
 8. The method defined by claim 7, wherein the entire quantity of fuel is accumulated in a storage cavity the entirety of which is on the face of the combustion chamber wall.
 9. A method of low pressure injection of ignitable fuel into the combustion chamber of a two cycle internal combustion engine operable through combined cycles of intake, compression, combustion and exhaust and which includes a reciprocating piston sealably movable between a cylindrical combustion chamber and a crankcase chamber to vary the volume thereof, an air inlet port opening on the cylindrical wall of the combustion chamber which communicates witH the crankcase chamber through an air transfer passage and an exhaust port opening on the cylindrical wall of the combustion chamber which communicates with atmosphere, comprising: a. accumulating a discrete quantity of fuel sufficient to produce engine combustion in a storage cavity the entirety of which is disposed on the face of the combustion chamber to permit free and instantaneous discharge of the entire quantity of fuel therefrom into the combustion chamber, said quantity of fuel being metered through the storage cavity as a function of pressure in the crankcase chamber and accumulated in the storage cavity at a time other than during the intake cycle; b. blocking fluid communication between the combustion chamber and the storage cavity for a time other than during the intake cycle; c. establishing fluid communication between the combustion chamber and the storage cavity during the intake cycle to release the entire accumulated quantity of fuel from the storage cavity and permit its free and instantaneous discharge into the combustion chamber; d. and supplying air to the combustion chamber separately from the accumulation of said quantity of fuel, said quantity of fuel and air being substantially mixed in the combustion chamber for ignition and combustion therein.
 10. The method defined by claim 9, wherein the quantity of fuel is accumulated in the storage cavity relative to the piston so that the piston blocks and establishes communication between the combustion chamber and the entire quantity of fuel. 